1. Field of the Invention
The present invention relates to plasma processing systems. More specifically, the present invention relates to plasma sources used for plasma etching, chemical vapor deposition, photo-resist stripping and other applications relating to semiconductor, flat panel display, printed circuit board and other fabrication processes.
2. Description of the Related Art
Plasmas sources capable of uniform coupling of electromagnetic energy to plasmas are needed for many plasma processes such as plasma etching, plasma enhanced chemical vapor deposition, physical vapor deposition, photo-resist stripping and surface treatments for many applications. Illustrative applications include silicon and compound semiconductor fabrication, flat panel display fabrication including active matrix liquid crystal display, plasma display panels, field emission displays etc. Additional applications include hard disk drive head and media manufacturing, micro-electromechanical system manufacturing and printed wiring board fabrication.
A plasma source typically includes a radio frequency antenna, a dielectric window and a volume of gas. An electric field from an impedance matched power supply is applied to the gas by the antenna through the dielectric tube. The application of the electric field to the gas generates two fields of interest with respect to plasma processing: time varying electromagnetic fields and capacitive electric fields. Free electrons gain energy by these electromagnetic fields and generate ions by collision with neutral gases, thereby generating plasmas. The inductive technique using a time varying electromagnetic field is known to be more efficient in the production of plasma than the capacitive coupling technique using a capacitive electrostatic field. A typical plasma etcher uses an additional electric field capacitively coupled to the substrate to increase ion energy.
Inductively coupled plasma sources typically use an antenna wound in circular spiral shape with an input terminal for receiving electromagnetic power at one end of the antenna and an output terminal for grounding at the other. This type of antenna induces a large potential difference between input and output terminals resulting in strong electric fields. Ions and electrons gaining energy through the interaction with these fields cause non-uniformity in the spatial energy distribution of plasmas which adversely impacts process results.
Hence, there is a need in the art for a system or technique for uniformly coupling electromagnetic energy for inductive generation of uniform plasmas. This need is addressed by the above-identified parent application of which this application is a continuation-in-part. However, a need remains for further improvements in the distribution of electromagnetic energy for inductive generation of uniform plasmas.